Underwater growth inhibition

ABSTRACT

To inhibit marine growth on a submerged framework, one or more collars are placed loosely around each member of the framework, the collars having outwardly projecting vanes so that ambient water movement causes movement around or along the member. The vanes (5; 25; 45; 55; 65) are preferably hinged to the collar for limited pivotation and may be twisted or provided with extension portions to ensure axial movement.

The invention relates to the inhibition of underwater growth.

Objects which are submerged in the sea for considerable periods aresubject to marine growth. In the case of the support structure of oiland gas rigs, substantial marine growth is very disadvantageous, becauseits weight places extra stresses on the structure, and because it altersthe original design profile so changing the design stress loadingcharacteristics. The marine growth must therefore be removed from timeto time, but removal constitutes a time consuming and therefore costlyoperation.

The present invention is concerned with the inhibition of underwatergrowth in a simple and convenient manner.

In accordance with the invention, there is provided a device arranged toextend around an underwater body, the device being responsive to ambientwater movement to move relative to the body so as to remove marinegrowth therefrom.

The invention also provides a method of removing underwater growth froman underwater body in which the body is surrounded by a deviceresponsive to water movement to move over the surface of the body tothereby brush away any underwater growth that has settled on thesurface. The body will typically be an elongate body, for example acircular cylindrical pipe, which will be encircled by the device of theinvention and cleaned of underwater growth by axial and/or rotationalmovement of the device.

The device can comprise a ring or collar having external vanes or otherpropulsion configurations responsive to ambient water movements to causemovement of the ring or collar around and/or along the body about whichit is placed. The propulsion vanes or fingers are preferably hinged tothe collar, advantageously so as to lie substantially tangentially whenlocated on one side of the body, thus presenting little drag, and so asto project outwardly on the other side, thus presenting a greater drag.When projecting outwardly, the vanes preferably extend subatntiallyradially and this position can be defined by a stop acting between eachvane and the ring or collar. Axial movement of the device is obtained byproviding the vanes with a twisted configuration or with a laterallyextending tab or finger.

The ring or hoop may also be configured on its inner side so as topromote the displacement of growth from the surface of the surroundedbody. The minimise the possibility of jamming of the device on theobject, the inner surface of the ring or collar can be convex, forexample, semi-circular or otherwise outwardly curved in radialcross-section.

The device can conveniently be manufactured of a suitable plasticsmaterial in the form of an elongate strip with spaced configurations bymeans of which the ends of an approrpriate length can be connectedtogether to form a ring. The propulsion means of the device can beconstituted by integral portions of such elongate strip material, theportions being partially separated from the adjacent material and hingedoutwardly from it.

The device of the invention can conveniently be made in two materials ofdifferent specific gravities, so as to float and sink in waterrespectively. The propulsion configurations can be shaped and/orarranged so that the floating device tends to travel in a downwarddirection in response to the action of ambient tides and current, whilstthe sinking device tends to travel upwardly. During still waterconditions, the devices float and sink to end positions, normallydefined by connections of the elongate body about which they extend toother elements of the structure, but on the resumption of watermovement, they move towards each other, and brush off small and immaturegrowth from the element as they do so. The provision of two such deviceson each body or length of body ensures that, the cleaning effect ismaintained by one should the other become detached.

The invention will be more readily understood from the followingillustrative description and the accompanying drawing, in which:

FIG. 1 is a perspective view of material ready to be formed into a firstdevice embodying the invention;

FIG. 2 is a view of a detail of the material of FIG. 1;

FIG. 3 is a schematic plan view of a second device embodying theinvention in place around an elongate body;

FIGS. 4 and 5 are respectively partial axial and side views of a thirddevice embodying the invention;

FIG. 6 is a partial side view of a fourth device embodying theinvention;

FIG. 7 is a partial plan view of a fifth device embodying the invention;

FIG. 8 is a partial exploded perspective view of the device of FIG. 7;

FIG. 9 is a partial cross-sectional view of the device of FIGS. 7 and 8;and

FIG. 10 shows devices embodying the invention, on a smaller scale, inplace on elongate elements of an undersea support structure for exampleof an oil or gas rig.

The material for forming a device in accordance with the invention shownin FIG. 1 comprises an elongate strip 1 of plastics material, preferablya fairly hard but resilient material, such as polypropylene. The body ofthe strip is of thin rectangular section and is provided with spacedrectangular slots 2 opening in from one side edge and spaced like slotsopening in from the other edge at positions between the slots 2.

By cutting off a length of the strip 1 so that there is a slot 2 at oneend of the length, for example as shown at the left hand end of FIG. 1,and a slot 4 at the other, a substantially circular cylindrical ring canreadily be formed by connecting the ends of the length together by meansof the slots. The width of the slots 2, 4 corresponds to the thicknessof the body of the strip, so that the two ends are frictionally heldtogether after assembly.

Between each adjacent pair of slots 2, 4, the strip 1 is provided with apropulsion vane or blade 5 of generally rectangular shape, with itslonger sides extending transverse to the strip material. Along one ofthese longer sides, the vane 5 is integrally connected with the stripmaterial by a hinge portion 6 formed to bias the vane to a predeterminedangular relationship with the body of the strip material.

To form a device 10 of the invention, the strip 1 is cut to anappropriate length for connection into a ring by means of the slots 2, 4as described, with the vanes 5 biassed outwardly.

The device 10 can be put in place around a horizontally extendingelongate element prior to submergence of the structure of which theelement forms in part, or in situ by divers, preferably after a cleaningoperation to remove existing marine growth where the structure has beensubmerged long enough for this to have become established. The device 10then turns on the submerged element in response to water movement, thevanes 5 being urged towards a tangential position when on one side ofthe element and towards a radial position, against the bias of the hingeportion 6 on the other.

To ensure that even water movement in a direction at right angles orparallel to the axis of the elongate element causes movement of thedevice 10 along that axis, as well as rotational movement, the vanes 5are profiled, as shown in FIGS. 1 and 2, so as to have an asymmetricalcross-section. The axial and rotational movements of the device 10 canof course be achieved in a variety of ways, for example, as by arrangingthe hinges 6 at an inclination to the length of the strip 1 instead ofat right angles to it.

The second illustrated device 20 according to the invention, shown inFIG. 3, again comprises a ring or collar 21 which may be formed fromstrip material in the same way as was the device 10. The device 20 haspreferably about eight vanes 25 spaced equally around the collar 21,each vane being freely hinged to the collar by a flexible hingeconnection member 26. The inner end of each vane 25 has a portion 27turned substantially at right angles to the plane of the vane, tofunction as a stop element.

When placed around a horizontally extending submerged elongate element30 of circular cross-section, and exposed to water movement in thedirection indicated by the arrow 31, rotation of the device 20 aroundthe element ensues, because of the operation of the vanes 25, as withthe vanes 5 of the device 10. Thus as shown in FIG. 3, the vanes 25 onthe upper side of the element 30 are caused by the water flow to move toa substantially tangential position, with the stop portion 27 extendinggenerally radially. As they reach the downstream side of the element 30,the vanes 25 begin to turn outwardly on the hinge members 26 until onthe lower side of the element 30 they extend substantially radially ofthe collar 21. The vanes 25 cannot pivot beyond this radial position,because of the engagement between the stop portion 27 and the outersurface of the collar 21.

In the third device 40 according to the invention partially shown inFIGS. 4 and 5, a collar 41 has rigid vanes 45, preferably eight innumber, pivotally connected to it by flexible hinge members 46. Eachhinge member 46 has a portion clamped to the outer surface of the collar40 by a stop member 47. A bolt 49 extends through aligned apertures inthe stop member 47 and the hinge member portion into a tapped hole inthe collar. The relatively rigid vane 45 is secured to a free endportion of the hinge member 46 as by rivets 44. The vane 45 may berectangular, but is preferably provided with at least one offset orlateral extension portion 42, which may be integrally formed with therest of the vane, so that the device experiences not only a rotationalmovement but also an axial movement, whatever the direction of the flowimpinging on the vanes. The extension portion 42 can be located at theouter end of the vane 45 as shown or elsewhere, for example, at theinner end of the vane, when the portion can function also as a stopelement.

FIG. 6 shows a fourth device 50 according to the invention, whichgenerally resembles that shown in FIGS. 4 and 5, but in which each vane55 is hinged to a ring or collar 51 and is formed with a twist along itslength. The twisted vane configuration functions, in place of thelateral extension portion 42 of the vane 45, to ensure that the device50 experiences axial movement.

As appears from FIG. 5, the collar 41 has a rounded, convex, innersurface, to minimise any tendency of the device 40 to jam on theunderwater element 30. In the device 50, shown in FIG. 6, jamming isprevented similarly by the semicircular cross-section of the collar 51.

A fifth device 60 according to the invention, shown in FIGS. 7, 8 and 9,has a collar 61, which is shown in all three Figures as a flat strip,that is, in the condition in which it is manufactured. The strip can bemoulded from a suitable plastics material with uniform thickness andwith interlocking formations by which the ends are joined together,preferably so as not to be thereafter separable, to form the collar ofthe device. Such end formations are shown in FIG. 7 as a dividedarrowhead 62 at one end of the strip and, at the other end, a tunnel 64through which the arrowhead can be pushed until the barbs of thearrowhead expand into a wider cavity beyond the far end of the tunnel,to securely connect the ends together.

The device 60 includes a plurality of rigid vane members 65, preferablyeight in number, each having a hinge portion 66 received in anappropriately shaped hinge recess integrally formed in the collar, aswill be seen from FIGS. 8 and 9.

The hinge recesses are provided in transverse ridges 70 of approximatelytriangular formation, equally spaced around the outer surface of thecollar. Each recess is formed as a transverse part-cylindrical pocket 71along the upper part of one side face of each ridge, the pocket edgesbeing defined by a first abutment surface 72 extending in a generallyradial plane and a second abutment surface 74 extending generallytangentially. The pocket 71 is limited at its end by side wall portions75.

Each vane member 65 comprises a rectangular vane portion 76 integrallyconnected with the rod-like hinge portion 66 by a neck portion 77extending from one of the vane portion shorter edges. The hinge portion66 makes a snap fit in the pocket 71 and when so received, the vanemember is free to pivot on the hinge portion between end positionsdefined by engagement of the abutment 72, 74 by the neck portion 77, inwhich positions the vane portion 76 extends generally radially of thecollar and generally tangentially, respectively.

The device 60 can be readily modified if required, for example, so thatthe range of movement of the angular movement is greater or smaller thanas indicated by the arrow 80 in FIG. 9. The shape of the vane portion 76can be other than a planer rectangular shape, for example, the vaneportion can be twisted as shown in FIG. 6 and/or provided with one ormore offset portions providing rotational movement and/or functioning asstop elements, similarly to the offset portion 42 of FIG. 5. The stripforming the collar can have a cross-section similar to that shown inFIG. 5 or FIG. 6 and its ends can be connected by other means than theinterlocking formations shown.

However a device embodying the invention is constructed and configured,it preferably has eight vanes evenly spaced around and the ratio of thecollar internal diameter to external diameter of the underwater elementor body which it surrounds is preferably in the range of 1.1 to 1.3. Theratio of the length of the vanes to the diameter of the underwater bodyis preferably in excess of 0.4 and the vanes are preferably arranged topivot outwardly to a position in which they make an angle in the rangeof 60° to 90° to the tangent at the position of connection to thecollar.

FIG. 10 shows part of an undersea support structure typical of thestructures of which devices of the present invention can advantageouslybe applied. The illustrated structure includes two generally verticallegs 101 connected together by generally horizonal struts 102 and aninclined strut 104.

To provide adequate protection against marine growth on the horizontaland inclined struts 102 and 104, these struts can each be fitted with atleast one device 105 embodying the invention for example the devices 20illustrated in FIG. 3, the device 40 of FIGS. 4 and 5 without theextension portions 42, or the device 60 of FIGS. 7-9. The vanes of thedevices provide an effective means of rotation and performance can beimproved by making the devices at least approximately neutrally buoyant.As for axial movement, the devices move along the struts even when smallangles of the flow direction is at a quite small angle, for example 10°from the normal to the strut axis. The varying directions of tidalcurrents and superimposed wave action will normally provide the desiredaxial movement along the horizontal struts 102, and, for the inclinedstrut 104, a component of current velocity either up or down the strutwill cause corresponding motion of the device if this is neutrallybuoyant.

For the vertical legs 101, the devices 105 embodying the inventionrequires to have vanes given an angle of twist, or pitch, as shown inFIG. 6 or extension portions as shown in FIGS. 5 and 6.

At least one growth inhibiting device 105 in accordance with theinvention is provided on each length of each leg or strut along whichthe device is able to move, that is, on ech length between connectionsto other elements of the structure. Although, the beneficial effects ofthe invention can be obtained by a single device on each such length, itis prefered as shown to provide two devices. Should one of the devicesbecome inadvertently detached and float away, the other can traverse theentire length previously shared with the detached device, so that aneffective cleaning operation is still achieved.

I claim:
 1. A device for removal or inhibition of underwater growth onan elongate underwater body, said device comprising:a collar adapted toextend loosely around said elongate underwater body; a plurality ofrigid vane elements; a plurality of hinge means, each hinge meanshingedly mounting a respective one of said vane elements externally ofsaid collar for pivoting relative thereto, said vane elements beingconfigured so as to cause rotational movement of said device in responseto ambient water movement.
 2. The device of claim 1 further comprisingstop means limiting pivoting of each of said vane elements outwardlyfrom said collar.
 3. The device of claim 2 wherein said stop means limitsaid outward pivoting to a substantially radially directed position ofsaid vane elements.
 4. The device of claim 1 further comprising meanslimiting pivoting of each of said vane elements between a position inwhich said vane element is substantially aligned with a tangent to saidcollar at the associated one of said hinge means and a position in whichsaid vane element makes an angle in the range of 60 to 90 degrees tosaid tangent.
 5. The device of claim 1 wherein said hinge means permitpivoting of said vane element about respective axes substantiallyparallel to the axis of said collar.
 6. The device of claim 1 whereinsaid vane elements are substantially uniformly spaced around saidcollar.
 7. The device of claim 1 wherein said collar comprises a lengthof strip material having formations at the ends thereof, whichformations are adapted to interengage to form said collar.
 8. The deviceof claim 1 wherein said collar has an inner surfce which is convex inradial cross-section.
 9. The device of claim 4 wherein said vaneelements are each shaped so as to impart axial as well as rotationalmovement to said collar.
 10. The device of claim 9 wherein each of saidvane elements has a twisted configuration, being twisted about an axisextending away from said hinge means.
 11. The device of claim 10 whereinsaid rigid vane elements each comprises a vane portion and a lateralextension portion.
 12. The device of claim 1 wherein each of said hingemeans comprises a flexible hinge member and further comprising aplurality of bolts, each bolt extending through a respective one of saidhinge members into said collar, and means securing each of said vaneelements to a free end of a respective one of said hinge members.
 13. Incombination, an elongate underwater member of generally circularcross-section and at least one device for removal or inhibition ofunderwater growth on the member, said at least one device comprising agenerally circular hoop surrounding said member, and vane elementshinged to said hoop for pivoting relative thereto to extend outwardlytherefrom, said vane elements being shaped to cause movement of saiddevice around and along said member in response to movement of the waterin which said member is submerged.
 14. The combination of claim 13wherein the ratio of the internal diameter of said hoop to the externaldiameter of said body is in the range of 1.1 to 1.3.
 15. The combinationof claim 13 wherein said member extends generally upright and whereintwo of said devices surround said member, one of said devices beingadapted to float and the other of said devices being adapted to sink.16. The combination of claim 15 wherein said one of said devices has thevane elements thereof adapted to cause upward movement of said deviceand wherein the second of said devices has the vane elements thereofadapted to cause downward movement of said device.
 17. The combinationof claim 13 wherein the ratio of the length of said vane elements to thediameter of said underwater member is in excess of 0.4.
 18. Incombination, an elongate underwater member of generally circularcross-section and at least one device for removal or inhibition ofunderwater growth on the member, said at least one device combination ahoop extending around said member, and vane elements, pivotally attachedto and extending outwardly from said hoop, said vane elements beingshaped so that movement of the water in which said member is submergedcauses movement of said device axially of said member.
 19. Thecombination of claim 18 wherein said device has at least approximatelyneutral buoyancy.
 20. The combination of claim 18 wherein said vaneelements are shaped to cause rotational movement of said device aroundsaid member in response to movement of the water in which said member issubmerged.